McIntosh MC 2105 Restoration P5: Let’s Test The Caps We Removed & Start This Thing Up

In this video, we’ll test the capacitors we removed, flush the potentiometers with control cleaner and power up the amp for the first time since we began the restoration. Learn how to test capacitors. Is recapping necessary? Do you need to recap? Do you need to replace capacitors? Do you need to recap an amp? How to test for DC leakage.

#electronicsrepair #stereo #stereorepair #amplifier #mcintosh

[richpaul]

LOL, I like that special effect with the ticking clock when you were testing the multi-cap can! (around 8:25 in the video). There's no doubt of your expertise in the field of electronics, (and probably several other fields), but I have to believe that you also had quite a bit of experience in making instructional videos!

Seriously, these videos (not just the MC2105, but the Dynaco and every one I've watched so far), may sound unappealing to watch to many people who aren't that interested in electronics. I know many people who would cringe at the thought of watching this kind of video. However, if they started watching one of yours, they'd find the videos are presented in such a way that makes them want to continue watching because of the clarity in the explanations of what you're doing.

I really must say that they're a pleasure to watch and I wish I could watch more of them at a time. However, I have to use what I've learned before I forget it and then move on to the next video. Even then, I still replay the video several times to double check myself.

I don't want to risk harming the amp so I'm working slowly, carefully and keeping things as clean as possible. It was in a condition that I could have easily sold it for more than twice what I paid w/o ever having done any upgrading. However, that's if I ever wanted to sell it, (which I don't).

I bought this MC2105 at a ridiculously good price near the end of 2019 from the original owner. Actually, from his daughter because her father passed away a year earlier. It was interesting to hear her reason for not selling it sooner:

She told me that she thought her father bolted it down to the cabinet it rested on. It wasn't until a friend came and pointed out that there were no bolts coming up from underneath the thick wooden top of the cabinet that she started to question that theory.

The friend told her that the only way he could have bolted it down was by driving wood-lag bolts through the four amp legs from the inside the amp's bottom cover and down into the thick wooden cabinet table, LOL. That's when they decided to try lifting it and were astonished to find that it weighed nearly 70 lbs!
Rich

[SwanseaTitanFan]

When your finished you are going to have one heck of an amplifier.

[richpaul]

Hi Chris, Would DeOxit be a good choice for cleaning those same selectors and various controls? I have DeOxit F5 & D5 and a generic brand of Electronics lubricant.

[richardadelberg]

Can u check filter caps with a reg fig volt meter . I don’t have a cap tester and vm seems to have max of 200 uf?

[richpaul]

Do you think the Heathkit IT-22 can do the job checking the caps in the MC-2105 with reasonable accuracy? I have a shot at getting one for someplace between $50 & $75.
Rich

[richpaul]

(Please note that I posted this second comment before I realized that you had replied to the question regarding the DeOxit):

OK, I watched this video twice now, particularly the last section regarding the tests. As you mentioned in an earlier reply, you were having trouble with the Gain Pots and I can see that. In fact, I was concerned about that being a possible problem with my amp and reason for a softer left channel output than the right. I blamed it on channel balance, recording balance differences, and EQ balance differences but when it came down to it, my excuses couldn't explain some of the conditions.

McIntosh is awful proud of their Gain Potentiometers. "Brian", (Part tech at Mac), quoted me $80 for each Pot! However, I refused to comprise on these even though I could have bought 10 Gain Pots made in China for the price of one Pot from Mac.

I bought two gain pots from Mac and with $25 shipping, TTL came to just under $190. That's more than I paid for the Mac MC2105 Faceplate!

Anyway, the new Pots are 240K Ohms and the ones I'm replacing are still in the amp. In circuit, the old Pots were giving me very different resistance readings.

They both had about the same max resistance of about 215K Ohms, but the minimum resistance from the Left channel pot was 23.5 Ohms, while the minimum from the right was 117.5 Ohms. Again, I was testing them in circuit so I'll be retesting them after I take them out. Still, I would have expected the readings to be opposite, with the left channel having a minimum of 117.5 Ohms. (It's possible that I mixed myself up because the amp was upside down, but I thought I took that in consideration).

NOW: I don't have an Audi Generator. I DO have a Variac (0v-130V, 5 amp) and an oscilloscope, (as well as a signal function generator, if that helps). Do you think I can do a similar test that would offer the same ultimate information that you're after in the tests that your doing here (at about 17:40 in the video)?

I bought two 8 Ohm x 25W and two 8 Ohm x 100W dummy resistors to do some tests on my Open Reel decks and this amp. My point is that I would pipe the output signal through the resistors, (8 Ohm x 25W), into the left and right channels of the scope.
Thanks,
Rich

[thundata]

What wattage bulb do you use for your dim bulb tester?

[richpaul]

Hi,
You've been a great help to me on my MC2105 and you probably remembered that I've had no luck in finding a replacement multi cap can. As per your suggestion, I found the video you've released on the Dynaco amp, (Dynaco SCA-80Q Amplifier Kit Part 2), which I've yet to review for info on building a multi-cap terminal. However, I wanted to test that multi-cap can first and followed your suggestion to watch this part of the MC2105 video set.

I've spent hundreds on instruments & special tools to do this job as proficiently as I can. I really would like to avoid buying yet some more instruments for this job because it's likely that I won't use them again except for maybe a very far-away project recapping a Sansui AU919. I own an analog oscilloscope (BK Precision 2120) and a digital signal function generator.

In addition, I own an analog AC Meter and of course, a DVMM. between these four instruments, is there anyway I can use them to reliably test capacitors? The Heathkit IT-28 looks expensive enough for me to try and find some other way to accomplish this test.
Thank you,
Rich
PS You know, I haven't been able to find any indication of your name, (first or last). Not even on your Flux Condenser page and I'd rather not call out "Hey You" lol. I know that these days, any personal info can be just that much more leverage a scammer can use. However, if you prefer not to give your first name, could you give me an alias that I can refer to you as? (thanks again)

[sean-mayorga]

Those pots aren't available anymore. But you can make them out of two separate pots. I think I have the part numbers somewhere. In regards to the headphone being wired backwards, most 2105s are like that. They were built before the standardization many people swap them to today's standard. They might be out of phase too double check that.